Torque converter lockup clutch control for an automatic transmission

ABSTRACT

A torque converter lockup clutch is pressurized from a source of regulated line pressure through a lockup clutch control valve, which directs pressure to either of two passages to apply and release the clutch. The control valve is supplied with control pressure from a solenoid-operated valve that produces high and low fluid pressure states corresponding to commands to engage and release the lockup clutch. A second control pressure, opposing the effect of the solenoid-operated control pressure, is applied to the control valve when the vehicle operator manually selects certain gear ratios, principally the lowest forward and reverse gear ratios. A line pressure regulator valve produces line pressure whose magnitude is proportional to the magnitude of a control pressure representing a commanded engine torque output. The pressure produced when the vehicle operator manually selects low gear ratios is applied also to the main regulator valve, which produces a line pressure that varies linearly with engine torque control pressure and increases, in comparison to line pressure at all other gear ratios, when low gear ratios are selected. A converter regulator valve limits the level of line pressure directed by the main regulator valve to the converter clutch control valve.

BACKGROUND OF THE INVENTION

Our invention relates generally to automotive transmissions of the typedisclosed in U.S. Pat. Nos. 3,393,585; 3,613,484; 3,706,240; 3,714,836;U.S. Ser. No. 24,500 filed Mar. 11, 1987 and U.S. Ser. No. 927,624 filedNov. 6, 1984. All of these applications and patents are assigned to theassignee of this invention.

A torque converter lockup clutch is pressurized from a source ofregulated line pressure through a lockup clutch control valve, whichdirects pressure to either of two passages to apply and release theclutch. The control valve is supplied with control pressure from asolenoid-operated valve that produces high and low fluid pressure statescorresponding to commands to engage and release the lockup clutch. Asecond control pressure, opposing the effect of the solenoid-operatedcontrol pressure, is applied to the control valve when the vehicleoperator manually selects certain gear ratios, principally the lowestforward and reverse gear ratios. A line pressure regulator valveproduces line pressure whose magnitude is proportional to the magnitudeof a control pressure representing a commanded engine torque output. Thepressure produced when the vehicle operator manually selects low gearratios is applied also to the main regulator valve, which produces aline pressure that varies linearly with engine torque control pressureand increases, in comparison to line pressure at all other gear ratios,when low gear ratios are selected. A converter regulator valve limitsthe level of line pressure directed by the main regulator valve to theconverter clutch control valve.

If the solenoid control pressure that represents a command for lockupclutch engagement and disengagement is continually present, perhaps theresult of an electrical failure or control system malfunction, thepresence of the control pressure produced when the vehicle operatorselects manually a low gear ratio will overcome the effect of themalfunction and release the torque converter lockup clutch. This actionopens the torque converter and makes available to the transmission thetorque multiplication capacity of the torque converter. When thetransmission operates in its lowest gear ratios, the highest torquecapacity of the transmission is assumed. Therefore, in this mode ofoperation and with the torque converter controlled by the system of thisinvention, the torque multiplication capacity of the torque converter isassured regardless of the pressure state produced by thesolenoid-operated control valve.

GENERAL DESCRIPTION OF THE INVENTION

The transmission of the present invention produces four forward speedratios and a reverse speed ratio. The third speed is a direct driveratio; the fourth speed is an overdrive ratio. The fourth or overdriveratio is achieved by holding the sun gear of a first simple planetarygear unit and by driving a second gear unit from the output of the firstgear unit while clutching together rotary elements of the secondplanetary gear unit so they rotate in unison. The three lowest forwardspeeds are produced by automatic shifts because a first overrunningclutch driveably connects rotary elements of the first gear unit withouttorque multiplication or speed reduction. The second and a third gearunit cooperate to produce torque multiplication through selectiveapplication of clutches and brakes, which driveably connect and holdelements of the later gear units.

In the lowest speed ratio produced by automatic shifts, a secondoverrunning clutch holds against rotation the carrier of the third gearunit. A third overrunning clutch completes a drivable connection betweenthe sun gears of the second and third gear units and a brake, therebyholding against rotation these sun gears to produce the second speedratio in the automatic mode.

Engine braking effect results by engaging a coast clutch in the first,second and third speed ratios when these ratios are selected manually.However, a band brake is applied during operation in the second speedmanual mode to replace the effect of the second overrunning clutch andintermediate brake, which are operative when drive is from the engine tothe wheels but inoperative when the drive is from the wheels to theengine. In this way, the inherently low torque capacity of the brakeband is required only when torque levels are low, i.e., during coastingoperation, but the intermediate brake and third overrunning clutch carrythe higher torques during drive operation.

A manual valve alternately connects a source of regulated line pressureto a forward drive passage and to a reverse drive passage. A shift valvealternately connects these passages to an input port of a coast clutchvalve in accordance with the state of a solenoid-operated valve. Acontrol port of the coast clutch shift valve is pressurized either froma manual valve, when the gear is selected manually by the vehicleoperator, or from a source of on-off pressure control by operation of asolenoid. In accordance with the control pressure, the coast clutchshift valve either connects its input to a line connected to the coastclutch or vents the input coast clutch to a drain passage in the shiftvalve.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of a transmission according to this inventionshowing in the assembled condition a hydrokinetic torque converter, theclutches, brakes and gear units.

FIGS. 2a-2h are diagrams of the multiple-speed transmission showing inheavy lines the components that operate to produce each of the variousspeeds.

FIG. 3 is a table showing the engaged and disengaged states of hydraulicclutches and brakes and the driving and overrunning states of theoverrunning clutches for each speed and range in which the transmissioncan operate.

FIG. 4 is a table showing the states of solenoid-operated shift valves,a converter clutch valve and coast clutch valve for each speed and rangeof the transmission.

FIGS. 5a-5e show a hydraulic control system capable of engaging anddisengaging the hydraulic clutches and brakes of the transmission ofFIG. 1. The lines connecting the hydraulic components are labeledalphanumerically to indicate the hydraulic pressures in the lines foreach speed and range.

DESCRIPTION OF THE PREFERRED EMBODIMENT

1. Gear Units, Clutches and Brakes

Referring first to FIG. 1, one end of an engine crankshaft 10 isdriveably connected through the transmission to the power output tailshaft 12, which is adapted to be connected to the vehicle tractionwheels through differential, driveline, and axle assemblies. The maintransmission housing 22 encloses simple planetary gear units 16, 18, 20.Transmission housing 22 is bolted at its left-hand periphery to thecylinder block of an internal combustion engine and, at its right-handend, to the left-hand end of tail shaft extension housing 24, whichsurrounds output shaft 12.

Transmission housing 22 encloses a hydrokinetic torque converter 26,which includes a bladed impeller 28, a bladed turbine 30 and a bladedstator 32. The impeller, the turbine and the stator are arranged influid flow relationship in a common toroidal circuit. The impellerincludes a housing connected driveably to drive plate 34, which isbolted to the end of crankshaft 10. Turbine 30 includes a turbine hub 36splined to turbine shaft 38. Impeller 28 is connected to impellerhousing 40, which is journalled for rotation on a portion 42 of a pumphousing, which closes converter housing 22. pump housing 44 is bolted tohousing 22 and encloses gear elements of a positive fixed displacementpump 46, which serves as a pressure source for the control valve systemto be described with reference to FIGS. 5a-5e. A stator sleeve shaft 48extends from the pump housing 44 and supports the inner race 50 of aone-way clutch 52 whose outer race supports stator 32.

A torque converter lockup clutch 54 is splined at 56 to the turbine hub36 and carries a friction surface 58, located at its radially outer end,to driveably engage the torque converter cover 61, welded to theimpeller housing. Lockup clutch 54 is closed, locked, applied or engagedto complete a mechanical connection between the impeller and turbinewhen pressurized hydraulic fluid, contained in the torque convertercasing, forces friction surface 58 against the housing. The torqueconverter is opened, unlocked, released or disengaged so that ahydrodynamic driving connection exists between the impeller and turbinewhen pressurized hydraulic fluid is supplied through passage 63 betweenconverter cover 61 and friction surface 58 of the lockup clutch todisengage these surfaces.

Turbine shaft 38 is splined at 58 to the carrier 60 of the firstplanetary gearset 16, which includes sun gear 62, a set of planetarypinions 64 rotatably supported on carrier 60 and ring gear 66. Sun gear62 is driveably connected to a member 70 that is common to a coastclutch 72 and an overdrive brake 74. Ring gear 66 is driveably fixed toa drum portion 68 connected to intermediate shaft 76.

Overdrive brake 74 includes a set of clutch discs fixed to housing 22, aload block 78 fixed to housing 22, a set of clutch discs driveablyconnected to the outer surface of clutch member 70 and interposedbetween the discs affixed to the housing, a clutch piston 80displaceable hydraulically against the clutch disc assembly andhydraulic cylinder 82 containing piston 80, and a Belleville spring 84for returning piston 80 to the inactive position when hydraulic pressureis removed from cylinder 82.

Coast clutch 72 includes a set of clutch discs driveably connected tothe inner surface of clutch member 70, a load block connected to theinner surface of clutch member 70, a second set of clutch discsdriveably fixed to ring gear 66, piston 86 actuated hydraulically toengage the coast clutch disc sets, a hydraulic cylinder 88 within whichpiston 86 moves, and a Belleville spring 90 to return piston 86 to thedisengaged position when hydraulic pressure is removed from cylinder 88.

A first one-way clutch 92 has its outer race driveably connected to ringgear 66, its inner race driveably connected by a spline to cylinder 88and to sun gear 62 and a driving member located in the annulus betweenthe inner and outer races for producing a one-way driving connectiontherebetween. A second one-way clutch 94 is located between intermediatebrake 96 and direct clutch 98. One-way clutch 94 includes an outer racethat carries a set of brake discs for the intermediate brake 96, aninner race driveably fixed to drum 100, and a driving member located inthe annular region between the inner and outer races for producing aone-way drive connection therebetween.

Intermediate brake 96 includes a second set of brake discs fixed tohousing 22, a load block fixed to the housing, a piston 101 actuatedhydraulically to force the brake disc sets into drivable relationshipagainst the load block, hydraulic cylinder 83 within which piston 101moves and a Belleville spring.

Drum 100 is stopped and held against the transmission casing through theaction of an intermediate brake band 102 actuated by a hydraulicintermediate servo. Direct clutch 98 operates to produce a driveconnection between drum 100 and clutch member 104. The direct clutchincludes a first set of clutch discs splined to the inner surface ofdrum 100 and a second set of clutch discs connected to clutch member104, and interposed between successive members of the first clutch discset. A piston 106 moves within a hydraulic cylinder to force the clutchdisc sets into drivable connection against the load block that iscarried on the inner surface of the drum 100. Piston 106 moves withinthe hydraulic cylinder defined by drum 100 and is restored to itsdisengaged position through operation of a coil compression spring 108.

Forward clutch 110 operates to produce a driving connection betweenclutch member 104 and the ring gear 112 of the second planetary gearset18. This gearset includes a sun gear 114, a set of planetary pinions 116in continual meshing engagement with sun gear 114 and ring gear 112,rotatably supported on a carrier 118 which is driveably connected byspline 120 to the tail shaft 12.

Forward clutch 110 includes a first set of clutch discs driveablyconnected to the inner surface of clutch member 104 and a second set ofclutch discs, each interposed with discs of the first set, driveablyconnected to the outer surface of ring gear 112. Piston 122 ishydraulically actuated for movement within the cylinder defined byclutch member 104 to force the clutch discs into a drivable connection.Belleville spring 124 returns piston 122 to the disengaged position whenhydraulic pressure is removed from the clutch cylinder.

The third planetary gearset 20 includes sun gear 126 formed integrallywith sun gear 114, ring gear 128 connected by spline 130 to tail shaft12, a set of planet pinions 132 rotatably supported on carrier 134,which is driveably connected to a first set of brake discs of thelow-and-reverse brake 136. A second set of brake discs of brake 136 isfixed to transmission casing 22; each disc of the second set isinterposed between successive discs of the first disc set of brake 136.Brake piston 138 is actuated hydraulically when cylinder 140 ispressurized to force the piston against the first and second brake discsets and to produce a drivable connection therebetween against theeffect of the return spring 142, which forces piston 138 to the brakedisengaged position when cylinder 140 is vented. Load block 144, fixedto the transmission casing reacts the force applied by piston 138 to thedisc brake sets.

A one-way brake 146 includes an outer race pinned to carrier 134, aninner race 150 bolted to the transmission casing 22, and a drivingmember located in the annular region between the inner and outer racesto produce a one-way drive connection between carrier 134 and thecasing.

The transmission produces four forward gear ratios and a reverse gear.The three lowest of the forward gear ratios are produced bothautomatically and by manual operation of the gear selector lever by thevehicle operator. The third forward gear ratio directly connects theengine crankshaft 10 to tail shaft 12, and the fourth forward ratio isan overdrive ratio. When the gear selection is made manually by thevehicle operator, the three lowest forward gear ratios and the reversedrive involve the engagement of coast clutch 72, and through itsoperation, the engine braking effect is transmitted through thetransmission to the tail shaft 12. FIG. 3 shows engaged and releaseconditions of the clutches and brakes and driving and overrunningconditions of the one-way clutches for each of the gears and ranges ofthe transmission.

The gear selector lever includes a prnd 21 switch, which produces anelectrical signal, preferably a voltage, whose magnitudes represent eachof the prnd 21 positions. The gear selector and the manual valve itcontrols can be moved among the following alphanumeric positions fromleftmost to rightmost: P for park, R for reverse, N for neutral, D foroverdrive, 2 for manually selected second gear, and 1 for manuallyselected first gear. When the gear selector is in the D position and anoverdrive cancel button is depressed, a mechanically selected conditioncalled "drive" range, the transmission will produce only the threelowest gears. When the button is released, and the selector is in the ODposition, a condition called "overdrive" range, the transmission canproduce four forward gears. When the gear selector is moved to themanual 1 or 2 positions, the transmission produces only the first orsecond gear ratios, respectively.

Coast clutch 72 produces engine braking in third gear when the gearselector is in "drive". Otherwise, the transmission would freewheel inthird gear while the vehicle is coasting. When overdrive range isselected, coast clutch 72 is disengaged hydraulically but engine brakingresults in fourth gear through operation of overdrive brake 74. Whenmanual 2 and manual 1 are selected, the coast clutch is appliedhydraulically; through operation of a coast clutch shift valve 302whereas, when drive is selected, the coast clutch shift valve isactuated through operation of a solenoid-actuated coast clutch valvecontrolled by programmed logic. A manually initiated shift from fourthgear to third gear or second gear causes a short delay to allowoverdrive clutch 74 to release fully before coast clutch 72 engages.

To prevent intermediate band 102 from absorbing excessive drivelineenergy in the manual 2 and manual 1 ranges, application of band 102 isdelayed until the coast clutch engagement is inferred by expiration of ashift-in-progress timer.

The torque flow in each gear and range is described next with referenceto FIGS. 2a-2h.

First Gear-Overdrive and Drive Ranges FIG. 2a

Low speed forward drive acceleration in the automatic mode is obtainedby engaging forward clutch 110. Torque then is delivered from turbineshaft 38 to carrier 60 of the first gearset 16. One-way clutch 92driveably connects ring gear 66 and sun gear 62 so that the entiregearset 16 turns as a unit and drives intermediate shaft 76. Torque isthen delivered from intermediate shaft 76 to the ring gear 112 throughengaged forward clutch 110, thus imparting a driving torque to carrier118 and the power output shaft 12. The reaction torque on sun gears 114,126 is in a reverse direction. This causes a forward driving torque onring gear 128, which is transferred to the output shaft 12 becausecarrier 134 acts as a reaction member. Carrier 34 is held againstrotation in this instance by overrunning brake 146.

In coasting operation, i.e. when torque flow is from output shaft 12toward shaft 38, OWB 146 overruns so that there is no torque path to thetorque converter.

First Gear Manual or 1 Range FIG. 2e

The vehicle operator selects low speed operation manually by moving thegear selector lever to the 1 position. In this range, forward clutch110, reverse-low brake 136 and coast clutch 72 are engaged, butconverter lockup clutch 54 is always disengaged. Clutch 72 connects ringgear 66 and sun gear 62, so gearset 16 again turns as a unit and drivesshaft 76. Shaft 76 drives clutch 110, which drives ring gear 112 andcarrier 118. Brake 136 provides the reaction by holding carrier 134,against rotation.

In coasting operation, the torque flow is from shaft 12 to shaft 76. Adrive connection to engine shaft for engine braking effect is completedfrom shaft 76 by coast clutch 72 and torque converter 26. Clutch 72 isapplied with the logic of the hydraulic circuit of FIGS. 5a-5e.

Second Gear-Overdrive and Drive Ranges FIG. 2b

Second speed ratio acceleration is achieved automatically by maintainingthe first gear status of the friction elements and by engagingintermediate brake 96. This holds sun gears 114, 126 against rotationbecause overrunning clutch 94 driveably connects brake 96 to drum 100.Powerflow from the engine to ring gear 112 is the same as that for thefirst speed overdrive and drive ranges. Planet pinions 116 driven byring gear 112 and rotate with carrier 118 about sun gear 114. Ring gear112 continues to act as a power input element and carrier 118 continuesto drive the output shaft 12. Overrunning brake 146 free wheels so thatall of the torque multiplication is accomplished by gearset 18.

During coasting, shaft 12 drives carrier 118 and pinion 116. Ring gear112 and clutch 110 rotating at engine speed cause OWC 94 to free wheelsin the coast direction, so the torque path ends there.

Second Gear Manual or 2 Range FIG. 2f

In the manually selected second speed, the following friction elementsare engaged: coast clutch 72, intermediate brake 96, forward clutch 110and intermediate band 102. In drive operation, clutch 72 connects ringgear 66 and sun gear 62, so gearset 16 turns as a unit and drives shaft76. Shaft 76 drives ring gear 112 through clutch 110. Overrunning clutch94 driveably connects sun gears 114, 126 to intermediate brake 96, whichholds sun gear 114; therefore, pinions 116 are driven by ring gear 112and rotate with carrier 118 about sun gear 114. Brake 96 is engagedbefore band 102 is applied, as will be explained below, so full enginetorque is not carried solely by band 102 but is stored with brake 96.

In coasting operation, clutch 94 overruns and shaft 12 drives carrier118 and pinions 116 about sun gear 114, which is held by band 102. Ringgear 112 drives shaft 76 and ring gear 66 through forward clutch 110.Gearset 16 turns as a unit because coast clutch 72 connects ring gear 66to sun gear 62. Therefore, pinions 64 and carrier 60 drive shaft 38,which is connected by the converter 26, or by converter clutch 54, toengine shaft 10.

Third Gear-Overdrive Range FIG. 2c

While accelerating in the overdrive range, third gear ratio results bymaintaining forward clutch 110 and intermediate brake 96 engaged and byengaging direct clutch 98. When the engine drives output shaft 12,overrunning brake 146 and overrunning clutch 94 freewheel, but one-wayclutch 92 drives. Shaft 76 and input shaft 38 turn at the same speed.One-way clutch 92 driveably connects ring gear 66 and sun gear 62 sothat turbine shaft 38 is driveably connected by the first gearset 16 tointermediate shaft 76. Direct clutch 98 and forward clutch 110 driveablyconnect ring gear 112, sun gears 114, 126 and intermediate shaft 76,which rotate as a unit. Planet pinion set 116, carrier 118 and outputshaft 12 are driven at the speed of the turbine shaft because of theconnection between ring gear 112 and sun gear 114. Overrunning brake 146free wheels. When the vehicle coasts, OWC 92 freewheels; therefore, ringgear 66 and sun gear 62 are disconnected and no engine braking effectoccurs.

Third Gear Manual or Drive Range FIG. 2g

When the overdrive cancel switch is closed on the gear selector to placethe transmission in the drive range, the friction elements operate asthey do to produce third gear in the overdrive range except that coastclutch 72 is engaged The transmission produces a direct connectionbetween input shaft 38 and output shaft 12, as in third gear overdrive,except that clutch 72 connects ring gear 66 and sun gear 62 instead ofOWC 92.

When the vehicle coasts, clutch 72 remains engaged, gearset 16 driveablyconnects shafts 76 and 38, and the torque converter connects shaft 38 toengine shaft 10.

Fourth Gear Overdrive Range FIG. 2d

The fourth gear ratio is achieved by maintaining forward clutch 110,direct clutch 98 and intermediate brake 96 engaged and by engagingoverdrive brake 74. Sun gear 62 of gearset 16 is held against rotationby brake 74 and one-way clutch 92 freewheels due to the engagement ofoverdrive brake. In this instance, ring gear 66 and intermediate shaft76 are driven at a higher speed than turbine shaft 38 and carrier 60.Gearsets 18 and 20 are disposed in the same condition as they were forthe third gear ratio in the automatic mode; therefore, the speed of theoutput shaft 12 is the same as the speed of the intermediate shaft 76.

In coasting operation, overdrive brake 74 remains engaged and the torquepath from output shaft 12 to engine shaft 10 is completed by gearset 16and the torque converter. Engine braking is therefore operative.

Reverse Gear FIG. 2h

Reverse drive is achieved by releasing intermediate brake 96, forwardclutch 110 and overdrive brake 74 and by applying low and reverse brake136, direct clutch 98, and coast clutch 72. With the friction elementsso disposed, one-way clutch 94 free wheels, one-way clutch 92 isinactive and one-way brake 146 is inactive. Coast clutch 72 driveablyconnects sun gear 62 and ring gear 66 of the first gearset 16 so thatturbine torque is delivered from shaft 38 directly to sun gears 114,126. With carrier 134 acting as a reaction point, ring gear 128 andpower output shaft 12 are driven in a reverse direction.

The transmission will produce upshifts and downshifts among the threelowest gear ratios in the drive range, and among all four gear ratios inthe overdrive range. Engine braking occurs in the highest gear availablein each range i.e., 1, 2, drive and overdrive. The schedule of FIG. 4shows the status of the coast clutch solenoid in each gear of each rangeand the availability of engine braking.

2. Hydraulic Circuit

FIGS. 5a through 5e show the hydraulic control valve system thatcontrols application and release of the hydraulic clutches and brakes ofthe change-speed gear box of FIGS. 1 and 2. The various passages arepressurized in accordance with selected positions of a manual valve 160,moved manually by the vehicle operator among six positions P, R, N, OD,2 and 1, and states of certain solenoid-operated valves as determined bymicroprocessor execution of control algorithms.

Fluid required for the operation of the hydraulic control valve systemis supplied at the output of a hydraulic pump, which is supplied fromthe sump or reservoir of the transmission through a filter or from areturn line connected to the inlet of the pump. The pump may be a fixeddisplacement pump that produces a flow rate proportional to its speed.

Line Pressure Regulation

Line pressure magnitude is controlled by main regulator valve 162 shownin FIG. 5a. This valve operates in response to a second control pressurecarried in line 164 from TV pressure valve 166. Valve 166 is connectedby passages 168 and 170 from regulated line pressure produced by mainregulator valve 162. A variable force solenoid 172 regulates TV pressurein accordance with commanded torque output by the engine by havingapplied across its winding an electrical voltage duty cycle inaccordance with the control of the microprocessor output. Hydraulicpressure having a magnitude between 5 psi and 85 psi produced by valve166 is applied to the end of line regulator valve 162. When there isdemand for a high volume of fluid at line pressure, spool 173 movesdownward due to TV pressure operating against the effect of a set ofcoil springs 174, closes the return line to the suction side 45 of thepump 46, and closes torque converter charge line 176. Then substantiallythe entire volumetric flow from the discharge side 47 of the pump iscarried in passage 170.

The magnitude of pressure in line 170 is a result of upwardly directeddifferential pressure on the lower end of spool 173 acting against thespring forces and a TV pressure force directed downward on the spool.When line pressure is high in relation to TV pressure, spool 172 movesupward and opens the feedback line to the suction side of the pump.Before this occurs, however, line 176 to converter regulator valve 178is opened. Thus, line pressure is regulated by balancing the springforces and TV pressure against line pressure in passage 170.

When manual valve 160 is moved to the 1 and R positions, line pressureis carried in passages 180, 182 to a differential pressure area of themain regulator valve. The pressure developed on the differential areaoperates to force spool 173 downward so that line pressure is higherwhen the reverse and 1 ranges are selected than for any of the othersettings of the gear selector and manual valve. Higher line pressure inthese ranges increases the torque capacity of the clutches and brakesengaged to produce the first gear and reverse drive while engine torqueis near its peak magnitude.

Solenoid-Operated Valves

Passage 170 carries line pressure to solenoid regulator valve 184, whichproduces a regulated solenoid feed pressure carried in passage 186 tofirst and second solenoid-operated shift valves 188, 190, a converterclutch solenoid-operated valve or first control means 192, and coastclutch solenoid-operated feed valve 194. Regulator valve 184 maintainsthe output in line 186 at approximately 50 psi by balancing spring forceapplied to the spool against an opposing line pressure force on thespool end resulting from feedback output.

Valves 188, 190, 192 and 194 are on-off valves that alternately connectand disconnect line 186 and output lines 196, 198, 200 and 202,respectively. The solenoids that operate these valves are controlled bythe output of the microprocessor, which selectively energizes anddeenergizes the solenoids in accordance with the result of executingelectronically stored control algorithms accessible to themicroprocessor. For example, when the solenoid of valve 188 isdeenergized, line 196 is vented by being connected to the low pressuresump. But when the solenoid is energized, solenoid feedline 186 isconnected to line 196. Similarly, valves 190, 192 and 194 either connectsolenoid feedline 186 to lines 198, 200, 202 or vent these lines inaccordance with the state of the corresponding solenoids.

Converter Clutch

Converter clutch 54 is engaged to lock torque converter 26 bypressurizing line 204 and venting line 206. The converter clutch isdisengaged and the torque converter opened when line 206 is pressurizedand line 204 is vented. Converter clutch control valve 208 moves upwardwithin the valve body due to a force on spool 210 resulting fromconverter clutch solenoid pressure carried in line 200, the source offirst control pressure. Valve 208 is forced downward by the helicalspring 211 and a pressure force resulting from 1-R pressure carried inline 180 to the upper end of spool 210. Also, control valve 208 issupplied through line 212 with regulated converter feed pressure fromconverter regulator valve 178, which regulates converter feed pressurein line 212 by sensing the pressure in line 212 and throttling convertercharge pressure in line 176. When converter clutch solenoid valve 192,and first control port 213 are energized, line 200 is pressurized, andspool 210 moves upward against the force of the spring 211 to connectlines 212 and 204. When this occurs, line 206 is connected by valve 208to vent port 214 and converter clutch 54 is engaged.

When solenoid valve 192 is deenergized, line 200 is vented causing spool210 to move downward, closing the connection between lines 212 and 204,closing the connection of line 206 to vent 214, and opening a connectionbetween lines 212 and 206. This vents line 204 through valve 208 and ahydraulic fluid cooler to the sump of the transmission. This actionopens the torque converter by disengaging the mechanical connection ofimpeller 28 and turbine 30 made through clutch 54. The 1-R pressure, inaddition to increasing line pressure for a given TV pressure, asdescribed with respect to the operation of valve 162, also operates toopen the torque converter if solenoid valve 192 remains open while thegear selector is moved to the 1 or R positions, perhaps due to failureof the solenoid that operates valve 192, a short circuit or otherelectrical fault. This 1-R pressure assures the torque converter will beopen if the gear selector is located in the R and 1 positions so thatthe torque multiplication effect of the converter is available tomaximize torque to output shaft 12. Converter regulator valve 178 limitstorque converter feed pressure to approximately 110 psi.

Line modulator valve 220 is connected to regulated line pressure bypassages 170 168 and 222, and to TV pressure by passages 164 and 224.

Automatic Forward Drive

Regardless of whether the OD cancel button is depressed on the gearselector mechanism, whenever manual valve 160 is moved to the ODposition, the position shown in FIG. 5d, regulated line pressure inpassage 168 is connected through valve 160 to passage 226. Forwardclutch 110 is continually connected to regulated line pressure throughpassage 226, orifice 342 and passage 242; provided the manual valve isin a forward drive position. First gear results for automatic shiftingwhen the forward clutch alone is engaged in this way.

In the OD range and with the transmission operating in first gear, firstsolenoid shift valve 188 directs SOLl pressure to 1-2 shift valve 228through passage 196 and to 2-3 shift valve 232 through passage 244, butsecond solenoid shift valve 190 is exhausted. Therefore, shift valves228 and 232 are moved by SOL1 pressure to the rightward extremity,closing line pressure passages 227 and 230, respectively. In this wayonly forward clutch 110 is pressurized and first gear operation results.

An upshift to second gear occurs while first solenoid shift valve 188remains open and after second solenoid shift valve 190 is opened. Valve190 directs SOL2 pressure through passage 198 to the end of 3-4 shiftvalve 236 and to manual timing valve 306. Passage 198 also directs SOL2pressure to shuttle valve 246. If passage 372 is not pressurized, valve246 directs SOL2 pressure to manual transition valve 250. If L/R clutchpressure passage 320 is not pressurized, transition valve 250 directsSOL2 pressure to the spring end of 1-2 shift valve 228. The 1-2 shiftvalve is moved leftward by SOL2 pressure, thereby opening the connectionbetween passages 227 and 254, through which regulated line pressure iscarried to intermediate brake accumulator 256.

Line Modulator and Accumulator

Line modulator valve 220 and accumulator work cooperatively to supplypressurized fluid to intermediate brake 96 thereby engaging second gear.Line modulator valve 220 supplies TVLM pressure to intermediate brakeaccumulator 256, overdrive clutch accumulator 260, and direct clutchaccumulator 262. Each accumulator is shown with its plunger located asit is prior to an upshift and filled with hydraulic fluid supplied fromvalve 220.

Valve 258, located immediately above accumulator 256, balances thespring force against intermediate brake pressure and moves upwardconnecting passages 254, 261. The upper end of accumulator 256 is filledthrough orifice 264. The orifice establishes a constant pressure dropand flow rate into the upper end of the accumulator cylinder and movesthe plunger downward at a rate consistent with the flow rate throughorifice 264 against the force of the springs within the accumulator andTVLM pressure within the accumulator below the plunger. In this way, thepressure in passage 261 rises linearly and rapidly when valve 258 firstopens; thereafter, pressure in brake 96 increases linearly as timeincreases at a lower rate determined by the flow rate through orifice264 and the spring constant of the springs within the accumulator. Also,pressure in brake 96 has a magnitude for each unit of elapsed time thatvaries with TV pressure, as is explained below.

The output of valve 220 is TVLM pressure supplied to the space withineach of the accumulators below the plungers. Valve 266, located at thetop of the bore of line modulator valve 220, regulates by balancing TVLMpressure against the force of the inner isolator spring 268, a shortspring having a relatively high spring rate that prevents contactbetween spools 270 and 266 when spring 268 is fully closed. When TVpressure, carried in passages 164, 224 from VFS valve 166, isapproximately 6 psi or lower, spool 270 is held by the outer spring atthe lower end of the valve bore, and spring 268 does not touch spool266. In this range of TV pressure, passage 272 is vented through port269 because feedback TVLM pressure will have forced spool 266 downwardclosing communication between passages 222 and 272. When TV pressurerises above 6 psi, valve 270 rises off its seat against the effect ofthe outer spring. Spring 268 causes valve 266 to regulate because itmoves valve 266 upward causing TVLM pressure to rise by one unit foreach two unit increase of TV pressure above 6 psi. In this way, linepressure is modulated according to the magnitude of TV pressure producedby VFS valve 166 in accordance with the control of the microprocessor.

Accordingly, the pressures produced by accumulators 256, 260, 262increase linearly with time after the initial rapid rise in their outputpressures following their being pressurized from passages 254, 278 and280, respectively. The pressures produced by the accumulators are higherat a given time after their linear increase begins if TV pressure ishigh, and lower at that time if TV pressure is low, because TVLMpressure varies linearly with TV pressure above 6 psi.

During the upshift, TVLM pressure in line 272 remains substantiallyconstant because fluid forced from below the accumulator plunger brieflyand slightly raises the pressure force at the head of valve 266 andopens the connection between line 272 and the vent 269 in modulatorvalve 220. Then the pressure in line 272 falls and the opening to vent269 closes. This lost fluid is returned to the accumulator through line222 while the accumulator is being recharged. When the intermediatebrake is to be disengaged, for example, during a 2-1 downshift, theprocess for activating the accumulator is substantially reversed fromthat of the upshift. The 2-1 downshift occurs when line 254 is vented at384 through 1-2 shift valve 228 due to the presence of SOL1 pressure andthe absence of SOL2 pressure at that shift valve. Flow from the spaceabove the plunger of accumulator 266 through orifice 275 and theconstant spring rate of the accumulator springs again controls the rateat which the plunger rises within its chamber and the rate at which theaccumulator cylinder below the plunger is filled with fluid from line222 and line modulator valve 220. As the accumulator is being recharged,fluid within the accumulator cylinder above the plunger flows throughone-way check valve 274, and passages 263, 254. Check valve 277 directsfluid through 261 downshift orifices, and the fluid is vented through1-2 shift valve 228. Likewise, intermediate brake 96 is vented throughpassages 261, 254, the 2-1 downshift orifice and shift valve 228.

Intermediate brake 96 remains engaged for third gear and fourth gearduring automatic operation because 1-2 shift valve 228 connects passages227 and 254 for any combination of states of solenoid valves 188, 190except the first gear states.

Overdrive clutch accumulator 260 works, as accumulator 256 does, topressurize and vent overdrive clutch 74 through passage 276 during a 3-4upshift and 4-3 downshift. These upshifts and downshifts are initiatedby selectively pressurizing and venting passage 278 through 3-4 shiftvalve 236, as described below.

An automatic upshift from second gear to third gear occurs after firstsolenoid shift valve 188 is closed by deenergizing its solenoid, andmaintaining second solenoid valve 190 open, according to the schedule ofFIG. 4. Line pressure continues to be directed by manual valve 160through passages 226, 230 to 2-3 shift valve 232. Because of the absenceof SOL1 pressure, valve 232 moves to the position of FIG. 5e. This opensline pressure to passage 280 through which control valve 282 at the endof direct clutch accumulator 262 is pressurized. Direct clutch 98 isthereby pressurized rapidly over a first, short portion of itsengagement period, during which the clearances among the variouscomponents of the clutch are taken up. Thereafter, clutch 98 ispressurized at a linearly increasing pressure controlled by themagnitude of TVLM, the rate of flow through orifice 284, and the springconstant of accumulator 262, as has been previously described withrespect to accumulator 256, until the clutch is fully engaged. Clutch 98remains engaged during third gear and fourth gear operation because SOL1pressure is absent; therefore, 2-3 shift valve 232 maintains open theconnection between line pressure and accumulator valve 282.

An automatic 3-2 downshift occurs when solenoid valves 188 and 190 areboth on. Then SOL1 pressure forces 2-3 shift valve rightward so thatdirect clutch 98 is drained through passages 286, valves 282, passage280, orifice 283, shift valve 232, passage 290, 3-4 shift valve 236, andpassage 292 to sump through manual valve 160. This path to sump from thedirect clutch is continually open through the 3-4 shift valve 236regardless of the presence or absence of SOL2 pressure at valve 236.

An automatic upshift from third gear to fourth gear results whensolenoid valves 188 and 190 are both closed, whereby overdrive brake 74is engaged. When this occurs, 3-4 shift valve 236 is moved by its springto the position shown in FIG. 5d, whereby line pressure from the manualvalve is directed by passage 234 through the shift valve to passage 278.Control valve 286 at the end of overdrive accumulator 260 is moved byits spring downward so that brake 74 is pressurized through passage 276rapidly during the first, short phase of engagement of the brake duringwhich clearances among the components of a brake are taken up.Thereafter, pressure in brake 74 rises linearly with time according tothe control of TVLM pressure, the flow rate of fluid through orifice 288and the spring constant of the accumulator, as has been described withrespect to accumulator 256.

An automatic downshift from fourth gear to third gear occurs when SOL 2pressure is applied to shift valve 236. This action moves the valverightward opening a connection through passage 278, valve 286, passage276 and brake 74 to the vent port at shift valve 236.

Reverse Gear

When manual valve 160 is moved to the R position, line pressure inpassage 168 is directed to passages 180, through bypass loops 294, 295to passage 292, and passage 226 is closed to the source of linepressure. Thus, forward clutch 110 is disengaged. Solenoid valve 188 isopened to connect SRV passage 186 to SOL1 passage 196, but solenoidshift valve 190 is closed. SOL1 pressure is carried in passage 244 tothe end of shift 2-3 shift valve 232, and to the SOL1 port of 1-2 shiftvalve 228.

Passage 180 is connected to line pressure both when the manual valve ismoved to the R position and to the 1 position. 1-R pressure forces spool210 of the converter clutch control valve 208 downward, therebydirecting regulated converter pressure through valve 208 and passage 206to open converter clutch 54. This action assures that, if SOL3 pressure.which is limited to 50 psi, remains on while the gear selector or manualvalve is in the 1 or R position, there is sufficient pressure to pushspool 210 downward and open the torque converter. In this way, thetorque converter is opened when 1 or R positions are selected so thatthe torque multiplication capacity of the torque converter is availableduring these high torque conditions. Passage 182 carries line pressurefrom valve 208 to the main regulator valve 162 when the gear selector isin the 1 and R positions. This forces spool 173 downward, closes returnto the pump inlet, and directs more pump output to passage 170.

Passage 300 and one-way check valves 299, 301 direct 1-R pressure alsoto the end of coast clutch shift valve 302; Check valve valve 299 andpassage 304 carry 1-R pressure from the manual valve to manual timingvalve 306.

Because SOL2 pressure is absent, 3-4 shift valve 236 is in the positionshown in FIG. 5d. Therefore, when the manual valve is moved to the Rposition, shift valve 236 connects line pressure in passage 292 topassages 290, 310 and 318. Check valve 312 directs R pressure throughorifice 314 to the end of low/reverse modular valve 316, where apressure force acting on the valve in opposition to its spring, opens Rpressure in passage 318 to low/reverse brake passage 320. Low/reversebrake 136 is the first friction element to become engaged in the processof producing reverse drive.

The 3-4 shift valve 236 also connects R pressure in passage 318 to coastclutch shift valve 302 through passage 322. Control pressure to coastclutch shift valve 302 is directed from passage 300 through the checkvalve 301 to passage 324. Valve 302 moves leftward against the effect ofits spring due to 1-R control pressure and completes the connection frompassage 322 to passage 326, 328 and passage 331 to coast clutch 72,which is the second friction element applied during reverse driveengagement.

Manual Shift Timing Valve

When the manual valve is in the R position. 1-2 shift valve 228 connectspassages 310 and 332 through check valve 369. Manual timing valve 306includes a piston 361, which is forced into contact with retaining plate363 by SRV pressure forwarded from solenoid regulator valve 184 andmaintained at a constant pressure by that valve. A second piston 330 isbiased by a spring into contact also with retainer plate 363. First andsecond inlet passages 360, 362 supply 1-R/MAN2 pressure to timer valve306 from passage 304. An orifice 364, located in passage 362, controlsthe flow rate through that passage and through valve 306 during aportion of its operation. Thereafter, when the valve opens, the higherpressure in passage 360 is directed to outlet passage 366.

In operation, first piston 362 is forced by SRV pressure into contactwith plate 363. Second piston 330 is forced by the spring into contactwith the plate against feedback pressure in passages 366, 368 tending tohold spool 330 rightward. This closes passage 360 but permits flowthrough orifice 364 and passage 366 to feedback passage 368. Ball checkvalve 369 and passage 332 carry R pressure from 1-2 shift valve 228 totiming valve 306, but check valve 369 closes passage 332 when it is at ahigher pressure than passage 310. Therefore, R pressure in passage 332is directed by valve 306 immediately without delay to passage 334because R pressure forces valve spool 330 rightward and opens thisconnection;

The space immediately adjacent both sides of the retainer plate ispressurized through feedback passage 368. Because of the differentialpressure across its ends, piston 361 immediately moves for a shortperiod away from the plate against SRV pressure until piston 361 seatson the valve body at the left-hand extremity. After this occurs,pressure rises quickly in the annulus, within which the retainer plateis located, and piston 330 moves rightward, subject to the flow rateacross orifice 364, against the spring force until it becomes seated atthe right-hand end of the valve chamber. In this position, feedbackpassage 368 is open to passage 334, through valve 306 and passage 360 isopen also to passage 334 through passages 366 and 368. The operation ofthe manual timing valve, therefore, delays the occurrence of Delayed1-R/MAN2 pressure at 2-3 shift valve 232 by the period while piston 360moves from the right-hand end of its chamber to the left-hand end plus.the period while spool 330 moves rightward from plate 363 until valve306 opens.

Valve 306 assures that whenever the vehicle operator moves manual valve160 to the 1, 2 positions, a delay occurs before pressure from themanual valve is present at 2-3 shift valve 232. This produces a shortdelay, one or two seconds, before a downshift from third or fourth gearcan be made into second gear. For example, when a 4-2 downshift iscommanded by the vehicle operator by a manual shift to the 2 position athigh speed, the transmission will dwell for a period, the periodrequired for the manual timing valve to produce MAN2 pressure in thirdgear, before the downshift to the second gear is completed. In thirdgear drive range, coast clutch engagement produces the engine brakingeffect, whereas in second gear manual operation, intermediate band 102and servo 96 produce the engine braking effect. Torque capacity of theband and servo are much lower than torque capacity of the coast clutch.By avoiding an immediate high speed 4-2 downshift, torque loads areeventually placed on band 102 are lower than otherwise they would be.Similarly, high speed downshifts into first gear are delayed to avoidthe sensation of an abrupt downshift.

However, SOL2 pressure at the end of timing valve 306 increases thedelay, or the absence of SOL2 pressure or prevents entirely any delay inpressure being output from valve 306, depending on the magnitude of1-R/MAN2 pressure compared to SOL2 pressure, the force developed on thespring of valve 306, and the occurrence of SOL2 pressure.

When manual timing valve 330 is positioned at the right-hand endpressure in passage 332 is directed as R pressure to passages 334, 336to ports of the 2-3 shift valve 232. Also, R pressure is present at 2-3shift valve 232 at the end of passage 290. As a result of pressure inpassage 334, a differential pressure is developed on the spool of shiftvalve 232, which regardless of the effect of SOL1 pressure at the end ofthe spool, forces the spool rightward against the effect of the springto connect passage 290 to passage 280. Control valve 282 at the end ofthe direct clutch accumulator 262 is pressurized through passage 280 andcheck valve 338. In this way, application of direct clutch 98 is bothcontrolled to rise linearly with time through operation of accumulator262 and delayed with respect to engagement of low reverse brake 136 andcoast clutch 72. When the direct clutch is fully engaged, reverse driveis completed.

Forward Clutch Valve

R pressure from manual valve 160 is directed by passages 292, 310 alsoto the reverse port of the forward clutch valve 240. TV pressure also isdirected through passage 340 from variable force solenoid valve 166 tovalve 240. When TV pressure is high, as when transmission fluid is coldor the accelerator pedal is depressed substantially, valve 240 connectspassages 310 and 344. This action adds flow of hydraulic fluid throughvalve 240 to flow from accumulator 262.

If the manual valve is in the OD or D position, and throttle pressure ishigh, valve 240 moves leftward against the force of its spring and opensa connection between passage 238, which contains fluid at line pressurewhenever the manual valve is in the OD position, and passage 242 to theforward clutch. This action adds the flow of hydraulic fluid throughvalve 240 to the volume supplied through passage 226 and orifice 342during automatic operation in forward drive. Therefore, when ambienttemperature is low and the viscosity of the hydraulic fluid isrelatively high, TV pressure increases the flow to the forward clutchand to the direct clutch to produce forward drive and reverse driveoperation, respectively.

First Gear Manual

When first gear is produced manually by moving manual valve 160 to the 1position, the transmission operates in the first gear by engagingforward clutch 110, low-reverse brake 136 and coast clutch 72, openingfirst solenoid shift valve 188, and closing second solenoid shift valve190. In this position, the manual valve connects-passages 168 and 180,through bypass loops 294 and 295, outlets of manual valve 160, butpassages 292, 226 and 318 are disconnected from line pressure passage168. Converter lockup clutch 54 is disengaged and the torque converteropens through operation of the converter clutch control valve 208, mainregulator valve 162 and converter regulator valve 178, as was previouslydescribed with reference to reverse drive operation.

When manual timing valve 306 times out, passage 334 communicates Delayed1-R pressure to two ports of the 2-3 shift valve 232, which is movedrightward by the presence of SOL1 pressure at the lefthand end of thevalve. This action opens communication between passages 336, 350 to aport of the 1-2 shift valve 228. SOL1 pressure in passage 196 movesshift valve 228 rightward, thereby connecting passages 350 and 352.Low-reverse modulator valve 316 supplied with R/Manual 1 pressure inpassage 352, is moved leftward by its spring connecting passage 352 topassage 320, through which low reverse brake 136 is engaged.

When the manual valve 160 is in the 1 position, it directs line pressurefrom passage 168 through passage 226, orifice 342, and passage 242 tothe forward clutch 110.

The coast clutch is energized through the manual valve 160, whichdirects line pressure through passage 180, check valves 299, 301 andpassage 324 to coast clutch shift valve 302.

Line pressure directed by manual valve 160 through passages 226, 230 ispresent at a port of the 2-3 shift valve 232. The presence of SOLlpressure or Delayed 1-R pressure will have moved shift valve 232rightward, thereby closing vent line 356 and connecting lines 230 and358. The differential pressure on the spool of 3-4 shift valve 236produced by pressure in passage 358 opens a connection between linepassage 234 and coast clutch passage 322. Coast clutch shift valve 302moves leftward due to the presence of 1-R pressure at its righthand end,and connects passages 322 and 326 to coast clutch 72 through orifice 374and passage 331. Delayed 1-R pressure transmitted in passage 334 to 2-3shift valve 232 is also passed through valve 232, passage 350, 1-2 shiftvalve 228 and passage 352 to low-reverse modulator 316. Low-reversebrake 136 is pressurized from valve 316, as is described above.

Second Gear Manual

A manual shift to second gear results when the gear selector manualvalve 160 is moved to the 2 position and both shift solenoid valves 188and 190 are turned on. In this position, the manual valve connectspressure in passage 168 to passages 226, 372 and disconnects passages180, 292, 318 from line pressure. Forward clutch 110 is pressurized, asit is for each of the four forward gears, directly from the manual valvethrough passages 226, 242 and orifice 342.

The presence of SOL2 pressure at the end of 3-4 shift valve 236 movesthe valve rightward to open the connection between passage 234, whichreceives line pressure through passage 226, and passage 322, whichtransmits line pressure from shift valve 236 to coast clutch valve 302.Manual valve 160 directs MAN2 pressure through passages 372, directionvalve 299, passage 300, direction valve 301 and passage 324 to thecontrol end of the coast clutch valve. The presence of the controlpressure at valve 302 opens a connection between passages 322, 326 anddirects coast clutch pressure through orifice 374 and passage 331 tocoast clutch 72.

Whenever coast clutch solenoid valve 194 is on, SRV pressure isconnected through valve 194 to passage 202 and direction valve 301 ispressurized, thereby closing passage 300 and pressurizing the controlport of coast clutch valve 302 through passage 324. This action,therefore, engages the coast clutch by completing a connection betweenpassages 322 and 326 regardless of the state of the manual valve.

MAN2 pressure is directed from manual valve 160 through passage 372,direction valve 299 and passage 304 to passages 360 and 362, which leadto manual timing valve 306. When the delay period of the valve expires,MAN2 pressure is connected through the valve and passages 334, 336 tothe 2-3 shift valve 232. MAN2 pressure develops a differential pressurepresent at that shift valve, opens passage 230 to passage 358, which isclosed at 3-4 shift valve 236, and directs MAN2 pressure through line350 to 1-2 shift valve 228. The 1-2 manual transition valve 250, biasedupward by its spring because of the absence of low-reverse brakepressure in passage 371 and at its control port, directs MAN2 pressureto passage 252. MAN2 pressure adds to the effect of the spring at shiftvalve 228 and works in opposition to SOL1 pressure to move shift valve228 leftward, thereby closing the connection between passages 350, 352and opening a connection between passages 350, 380. MAN2 pressure isdirected through orifices 382, 383 to the intermediate servo 96.Orifices 382, 383 delay engagement of servo 97 so that intermediatebrake 96 is engaged shortly before servo 97, actuates band 102 and holdsdrum 100 against rotation. With the 1-2 shift valve so disposed, linepressure in passages 226, 227 and present at shift valve 228 isconnected by passage 254 to the control valve at the end of intermediateclutch accumulator 256, by means of which passage 260 and intermediatebrake 96 are pressurized in accordance with the technique describedabove. The delay in applying servo 97 and band 102 until after brake 96is applied assures that engine torque is not carried by band 100.

A manual downshift to first gear from second gear occurs after MAN2pressure is removed from the control end of the 1-2 shift valve. Thiscauses shift valve 228 to move rightward thereby closing the connectionbetween passages 350 and 380 to the intermediate servo 96, connectingpassages 350 and 352 to low-reverse brake 136 through the low reversemodulator valve 316, disconnecting passages 226 and 254, and connectingpassage 254 to vent port 384. In this way, intermediate brake 96 isvented and drained through accumulator control valve 258. The fluidabove the plunger of accumulator 256 passes through ball check valve 277to passage 254 and eventually the 2-1 downshift orifice near vent 384.

Third Gear Manual

When the manual valve is moved to the OD position and the drive buttonis depressed, the transmission will produce automatic shifts among thefirst three gears in the manner previously described with respect toautomatic operation. However, in this case, unlike overdrive operation,third gear has engine braking effect due to engagement of the coastclutch. Intermediate brake 96, direct clutch 98, and forward clutch 110are applied as described above with respect to overdrive operation. Toproduce third gear, second solenoid shift valve 190 is on and firstsolenoid shift valve 188 is off. The 3-4 shift valve 236, movedrightward by SOL2 pressure, opens a connection between passage 234 andcoast clutch pressure in passage 322.

Coast Clutch Shift Valve and Solenoid Valve

When a command is made for third gear operation and the manual valve isin the overdrive position with the drive range button depressed, coastclutch solenoid valve 194 is on and it directs SOL4 pressure throughpassage 202. Check valve 301 pressurizes the control port of coastclutch shift valve 302. This moves shift valve 302 leftward and connectscoast clutch pressure in passage 322 to passage 326, through which coastclutch 72 is engaged, whereby the transmission is disposed for operationin third gear with engine braking.

To upshift from manual third gear to fourth gear coast clutch 72 isdisengaged and overdrive clutch 74 is engaged. To disengage the coastclutch, 3-4 shift valve 236 moves leftward when SOL2 pressure isremoved, thereby closing the connection between line pressure in line234 and passage 322 and connecting passages 234 and 278. Overdrive brake74 is engaged through operation of accumulator 260. In this way, coastclutch shift valve 302 will not supply pressure to the coast clutch evenif SOL4 pressure is available at the control port of coast clutchpassage 326. In making the upshift from third gear manual to fourthgear, SOL4 pressure is removed permitting the valve 390 to close passage322 and to connect coast clutch 22 to vent port 390.

Having described a preferred embodiment of our invention, what we claimand desire to secure by U.S. Letters Patent is:
 1. A converter lockupclutch system controlling an automatic transmission torque converterhaving an impeller adapted for driveable connection to an engine and aturbine hydrokinetically driveable connected to the impeller,comprising:a torque converter clutch for alternately locking andreleasing the impeller and turbine, having a first passage carryingconverter release pressure to unlock the clutch and a second passagecarrying apply pressure to lock the clutch; a source of line pressure;manual valve means for connecting the source of line pressure to anoutlet when a low gear ratio is selected manually by a vehicle operator;first control means for producing first control pressure statesrepresenting commands to release and to apply the torque converter; anda converter clutch control valve means communicating with the outlet,the first control means and the source of line pressure when the firstcontrol means produces the converter release pressure state, forconnecting the second passage to the source of line pressure when thefirst control means produces the converter apply pressure state, and forconnecting the first passage to the source of line pressure when saidlow gear ratio is selected regardless of the pressure state produced bythe first control means.
 2. The system of claim 1 further comprising:ahydraulic pump having a low pressure inlet and a discharge; secondcontrol means for producing a second control pressure having a magnitudethat varies according to commanded torque output of the engine; mainregulator valve means communicating with the outlet, the second controlmeans, and the pump discharge for connecting the pump discharge to thesource of line pressure and for regulating the magnitude of linepressure in accordance with the magnitude of the second controlpressure.
 3. The system of claim 2 wherein the main regulator valvemeans further includes means for increasing the magnitude of linepressure when the outlet is pressurized, in comparison to the magnitudeof line pressure produced when the outlet is unpressurized.
 4. Thesystem of claim 2 further comprising converter regulator valve meanscommunicating with the source of regulated line pressure for producing asource of limited magnitude line pressure and for connecting the limitedmagnitude line pressure to the converter clutch control valve means. 5.A method for controlling a torque converter having an impeller adaptedfor driveable connection to an engine and a turbine hydrokineticallydriveably connected to the impeller for use in an automatic transmissionthat includes a source of line pressure, comprising the stepsof:connecting a source of line pressure to an outlet when a low gearratio is selected manually by a vehicle operator; producing firstcontrol pressure states representing commands to release and to applythe torque converter; connecting a first passage to a source of linepressure when a first control means produces the converter releasepressure state; connecting a second passage to the source of linepressure when the first control means produces the converter applypressure state; connecting the first passage to the source of linepressure when said low gear ratio is selected, regardless of thepressure state produced by the first control means.
 6. The method ofclaim 5 further comprising:producing a second control pressure having amagnitude that varies according to commanded torque output of theengine; and regulating the magnitude of line pressure in accordance withthe magnitude of the second control pressure.
 7. The method of claim 5further comprising increasing the magnitude of line pressure when theoutlet is pressurized, in comparison to the magnitude of line pressureproduced when the outlet is unpressurized.
 8. The method of claim 6further comprising:producing a source of limited magnitude linepressure; and connecting the limited magnitude line pressure to theconverter clutch control valve means.
 9. A converter clutch controlvalve for an automatic transmission having multiple gears comprising:aspool moveable within the valve; a port communicating with a source ofline pressure; a vent port; passages connecting the valve and the clutchincluding a first passage carrying converter release pressure to unlockthe clutch and a second passage carrying converter apply pressure tolock the clutch; a first control port communicating with a source offirst control pressure having pressure states representing commands torelease and to apply the torque converter, the first control pressureurging the spool to a position where the valve opens communicationbetween the line pressure source and the second passage and openscommunication between the first passage and the vent port; spring meansurging the spool to a position where the valve opens communicationbetween the line pressure source and the first passage, and openscommunication between the second passage and the vent port; and a secondcontrol port communicating with a second control pressure when thetransmission operates in a predetermined gear, the second controlpressure urging the spool to a position where the valve openscommunication between the line pressure source and the first passageregardless of the state of the first control pressure, and closescommunication between the second passage and the line pressure source.